Understanding the Stars. How can we learn about the lives of stars, which last millions to billions of years? Consider the story of the Ephemera Image from: http://www.startunzflutes.com/graphics. How can we Study the Life Cycles of Stars?. A star can live for millions to billions of years.
Order of brightness within a constellation
Latin Genitive of the constellation
Our goals for learning:
Luminosity – the total amount of power radiated by a star into space.
App Bright = L / 4d2
The Inverse Square Law for Light
What Determines Apparent Brightness?
parallax – apparent wobble of a star due to the Earth’s orbiting of the Sun
p = parallax angle
d = 1 AU/ p
Gives distance in
convert p into arcsec
d = 206,265 AU/ p
1 parsec 206,265 A.U. = 3.26 light years
d = 1 / p
If p is in arcsec and d is in parsecs
A star with a parallax of 1 arcsec is 1 parsec distant
Astronomers still use an ancient method for measuring stellar brightness which was proposed by the Greek astronomer Hipparchus (c. 190 – 120 B.C.)
This scale runs backwards:
The bigger the number, the fainter the star
Brightest stars are #1, next brightest are #2, etc.
= -2.5 log (app bright)
1.26 (see chart of brightest stars at end of your text)
Deneb has an Absolute visual magnitude of -8.73
(this is about the same brightness as the quarter moon---but at 32.6 light years away!)
Using the weird equation, the distance to deneb can be calculated: 2500 light years (M – m = 5 – 5log(d))
One last obvious question: How did we ever know the Absolute visual magnitude to Deneb without knowing its distance in the first place?
Stars come in many different colors.
The color tells us the star’s temperature according to Wien’s Law.
Bluer means hotter!
Oh Be A Fine Girl/Guy, Kiss Me!
50,000 K 3,000 K